Rough idle 3.0si N52b30

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djd234

Member
Hi all. Since purchase of my car (z4 3.0si) I have been experiencing a rough idle that exists for 30-60s upon starting both hot and cold that smooths out. Unsure as to what’s going on. Had it smoke tested recently and a small leak fixed however the issue still persists and smoke tested showed clear. My fuel trims are negetive and have became more so after air leak fix. Engine data from hot idle after drive (not rough) is shown in the images attached taken a few minutes apart.

My guesses are maybe vanos, injectors or dodgy sensors ?
 

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Too rich (any fuel trim < 0%). Too much fuel, not enough air. Faulty MAF or Pre-Cat O2 sensor fooling the DME into thinking 1 of the 2 prior causes is happening, blocked Cats. If the problem is bank specific, a leaking injector.

Check your cats by looking at the post cat O2 signals with a hot engine at idle. The signals should be above 0.5V. Momentary dips below 0.5V are allowable.
 
NZ00Z3 said:
Too rich (any fuel trim < 0%). Too much fuel, not enough air. Faulty MAF or Pre-Cat O2 sensor fooling the DME into thinking 1 of the 2 prior causes is happening, blocked Cats. If the problem is bank specific, a leaking injector.

Check your cats by looking at the post cat O2 signals with a hot engine at idle. The signals should be above 0.5V. Momentary dips below 0.5V are allowable.
Click to expand...
Long term fuel trim values are:
Bank 1: -5 ish
Bank 2: -10 ish they fluctuate a little day to day
O2 signals appear to be 0.6-0.7 ish one of them flickery occasionally
Maf - 3.5 ish
These values all at warm idle after drive.

Upon start the MAF values spike to 7 ish warm start or higher when cold and drop slowly.

Odd is on cold start MAF is at 10 and drops slowly.

unsure if this will help paint a clearer picture
 
I have something similar going on with mine, but yet to identify it. Interested to know if I am getting similar readings.
Can I ask what app you are using in the screenshots above?

thanks
 
chanlon1 said:
I have something similar going on with mine, but yet to identify it. Interested to know if I am getting similar readings.
Can I ask what app you are using in the screenshots above?

thanks
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Hi, anything you’ve ruled out so far?
But the App being used is Carly. Bluetooth OBD dongle connects to your phone. However tbh I wouldn’t rly recommend it. Haven’t been that impressed I’d say it doesn’t do as much as it is implied it does. I’d say the GUI ect looks good however the functionality is t amazing. It is good for coding though
 
djd234 said:
Hi, anything you’ve ruled out so far?
But the App being used is Carly. Bluetooth OBD dongle connects to your phone. However tbh I wouldn’t rly recommend it. Haven’t been that impressed I’d say it doesn’t do as much as it is implied it does. I’d say the GUI ect looks good however the functionality is t amazing. It is good for coding though
Click to expand...
I've Carly aswell, but the screenshots didnt look familiar, hence why I was asking.
I'm planning on taking the injectors out and testing/cleaning to see if that helps.
New spark plugs were put in last year, so I am ruling them out
I havent done anything with the coil packs yet - its possible that I could go down the path of buying new packs.
Cleaned the MAF sensor, but I don't think it made any difference. (I disconnected the MAF when the engine was running and the car should have tried to work out itself what to do, but the engine fluttering/hunting was still there.
Still a bit convinced that it's due to a vacuum leak somewhere. I did make my own smoke tester machine, but nothing obvious was leaking when I tested it - I'm not 100% I was doing it right though.
 
chanlon1 said:
I've Carly aswell, but the screenshots didnt look familiar, hence why I was asking.
I'm planning on taking the injectors out and testing/cleaning to see if that helps.
New spark plugs were put in last year, so I am ruling them out
I havent done anything with the coil packs yet - its possible that I could go down the path of buying new packs.
Cleaned the MAF sensor, but I don't think it made any difference. (I disconnected the MAF when the engine was running and the car should have tried to work out itself what to do, but the engine fluttering/hunting was still there.
Still a bit convinced that it's due to a vacuum leak somewhere. I did make my own smoke tester machine, but nothing obvious was leaking when I tested it - I'm not 100% I was doing it right though.
Click to expand...
Odd how yours looks different. Mine only looks that way as I only seem to be able to get live data by going through ‘OBD functions’. Maybe you can help me there.
Vacuum leak is usually a good port of call for this sort of thing I was surprised when it isn’t for me. Do you also experience the petrol smell on start. I find that one most concerning. It’s pretty strong coming out the exhaust for a few seconds for me
 
djd234 said:
Do you also experience the petrol smell on start. I find that one most concerning. It’s pretty strong coming out the exhaust for a few seconds for me
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Could it be leaky injectors?
Have you tried taking the plugs out before you start, to see if any are wet?
 
enuff_zed said:
Could it be leaky injectors?
Have you tried taking the plugs out before you start, to see if any are wet?
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That’s actually my number one suspect due to mismatched trims and the smell combined with the short duration rough idle. Currently I don’t have the tools to hand to do this but some could be borrowed. I have done very little work on cars before but I hear this is easy?
 
djd234 said:
That’s actually my number one suspect due to mismatched trims and the smell combined with the short duration rough idle. Currently I don’t have the tools to hand to do this but some could be borrowed. I have done very little work on cars before but I hear this is easy?
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Pulling a plug is very easy.................. with the correct tools.
Where are you? Maybe someone close to you could assist?
 
enuff_zed said:
Pulling a plug is very easy.................. with the correct tools.
Where are you? Maybe someone close to you could assist?
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Portsmouth Southampton way. I’m having it checked at a garage on wedsnesday so I’m interested to see what they say. Oddly enough on the fuel trims side. After a couple days driving since last checked the LTFT are at bank 1 +3 bank 2 -3. Still the same 5-6% disparity but centered around 0. Wondering if since my Vac leak fix it’s taken a week or so to adjust itself
 
enuff_zed said:
Kept your head down today then? Hope there's no post-match trouble.
As a Pompey fan I ended up quite pleased with that result.
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More specifically, in Portsmouth. so I didn’t see too much trouble about. Heard Southampton was more so though…
 
djd234 said:
Do you also experience the petrol smell on start. I find that one most concerning. It’s pretty strong coming out the exhaust for a few seconds for me
Click to expand...
I used to have a strong smell of fuel inside the car, but that was due to the rocker cover gasket being crap.

As soon as I replaced it, fuel smell inside vanished.

Per the other comments above, my next step is to check the injectors.
 
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